The prior art already discloses connecting metal semifinished products which are coated on one side with at least one plastic layer to one another in order to form a sandwich composite material. For example, German laid-open specification 21 18 230 discloses connecting corresponding semifinished products which are coated with a plastic layer on one side in a discontinuous method in which the metallic side of the semifinished product is heated, so that the plastic layer softens and the two semifinished products are then pressed against one another by way of the plastic sides of said semifinished products, so that the plastic layers are connected to one another. In continuous methods, it is known, for example, to connect two strip-like semifinished products, which are coated with at least one plastic layer, by means of the plastic layers in order to form a sandwich composite material in which heat is introduced into the metallic covering layers of the semifinished products by means of a twin-belt press, so that the plastic layer softens and therefore a connection is made with the opposite plastic layer. One problem with introducing heat in order to activate the plastic layer is that, on account of the transportation of heat from the metallic covering layer of the semifinished product to the opposite side of the semifinished product, which side establishes the connection, relatively high temperatures have to be applied in order to reach the targeted temperature in the boundary region of the two plastic layers. In this case, there is a risk of the plastic layer melting and delaminating in the region of the metal because said metal is at a higher temperature than the plastic surface of the semifinished product.